A random sample of 1500 residential telephones in Phoenix in 1990 indicated that 387 of the numbers were unlisted. A random sample of 1200 telephones in the same year in Scottsdale indicated that 310 were unlisted. (a) Find a 95% conidence interval on the difference in the two proportions and use this conidence interval to determine 2010 whether there is a statistically signiicant difference in proportions of unlisted numbers between the two cities. (b) Find a 90% conidence interval on the difference in the two proportions and use this conidence interval to determine if there is a statistically signiicant difference in proportions of unlisted numbers for the two cities. (c) Suppose that all the numbers in the problem description were doubled. That is, 774 residents of 3000 sampled in Phoenix and 620 residents of 2400 in Scottsdale had unlisted phone numbers. Repeat parts (a) and (b) and comment on the effect of increasing the sample size without changing the proportions on your results.